A video purportedly showing an eagle swooping down and snatching a baby has gone viral:

Given how unlikely the video seems, there is a vigorous debate about its authenticity. We performed a forensic lighting analysis on this video to determine if it is real or fake.

To perform this analysis, we connect points on an object with their corresponding cast shadow. Because of the geometry of cast shadows, all such constraints must intersect at a single point. (For an understanding of why this is so, read my previous blog post about shadows.)

Shown below are five such constraints from one frame of the video, just as the eagle is about to the grab the baby. The red lines are from the baby and eagle, and the blue lines are from the slide, adult, and stroller. You can clearly see that these shadows are not consistent with one another. The most likely scenario is that the baby and eagle are computer generated and were inserted into a real-world scene. Because this scene is outdoors and illuminated with a single light source (the sun), there is no physically plausible explanation for this inconsistency in shadows.

[click for a magnified view]

[UPDATE: Minutes after posting this blog entry, we discovered that the perpetrators of the hoax had come forward. They managed to fool much of the internet pretty successfully, but it appears that they can still use some practice in refining their 3D simulations.]